A variety of medical diagnostic and other systems are known in which x-ray tubes are employed as a source of radiation. In medical imaging systems, for example, x-ray tubes are used in both x-ray systems and computer tomography (CT) systems as a source of x-ray radiation. The radiation is emitted in response to control signals during examination or imaging sequences. The radiation traverses a subject of interest, such as a human patient, and a portion of the radiation impacts a detector or a photographic plate where the image data is collected. In conventional x-ray systems the photographic plate is then developed to produce an image which may be used by a radiologist or attending physician for diagnostic purposes. In digital x-ray systems a photo detector produces signals representative of the amount or intensity of radiation impacting discrete pixel regions of a detector surface. In CT systems a detector array, including a series of detector elements, produces similar signals through various positions as a gantry is displaced around a patient.
Depending upon the particular modality of the imaging system and the system configuration, the x-ray tube source may be mounted in various manners. For example, in conventional x-ray systems, anode and cathode assemblies support the x-ray tube within a casing. The anode assembly is coupled to a target within a glass or metal envelope, while the cathode assembly is coupled to a cathode plate. A metal shield or casing surrounds the glass envelope. The volume between the casing and the envelope is filled with a cooling medium, such as oil. A window is provided in the casing for emitting x-rays created by controlled discharges between the cathode plate and the target.
The x-ray tube is typically operated in cycles including periods in which x-rays are generated interleaved with periods in which the x-ray source is allowed to cool. A typical imaging sequence may include a number of such sequences. Moreover, the x-ray tube may have a useful life over a large number of examination sequences, and must generally be available for examination sequences upon demand in a medical care facility.
Given the demanding schedules to which x-ray tubes are often subjected, failure of the tubes is of particular concern. Various failure modes have been observed in x-ray tubes, and these may have a variety of sources. For example, within the glass encasement a vacuum or near vacuum is preferably maintained. However, due to leaks, degradation in the cathode or anode materials, decomposition of anode filaments, and so forth, particulates may be created or freed within the tube. These particulates may result in eventual failure of the tubes over time. Failure of the tubes can also be a function of the modes of operation and user-selected parameters, such as voltage or current.
Due to the stringent requirements and reliability demands placed on x-ray tubes in medical diagnostic systems, special programs may be implemented for insuring rapid replacement of the tubes upon failure. Present procedures for replacement of x-ray tubes in medical diagnostic systems are primarily reactionary. Service personnel generally monitor the performance of the tubes over time and through the various examination sequences. However, the service personnel are often made aware of tube failures only as they occur. When a tube does fail, to insure rapid replacement of failed tubes a conventional response is to expedite shipment of a replacement tube which is then installed by trained service personnel at considerable shipping and handling expense. While the x-ray tubes could be shipped in advance and stored on location or in a centralized service facility, these strategies also require inventory of relatively expensive items, again resulting in additional costs of the service program. Such inventories may also inconveniently occupy valuable storage space at the location.
There is a need, therefore, for an improved management and servicing approach to x-ray tube replacement. In particular, there is a need for a service system which can reduce down time in diagnostic, imaging and other systems incorporating x-ray tubes as radiation sources which can result from an anticipated failure of the x-ray tubes. The system would advantageously permit forecasting of possible tube failure and scheduling of tube replacement and shipment prior to actual failure. Such a system could also provide feedback for planning the tube manufacturing and assembly process, as well as feedback to system users for planning the replacement process.